Cuttlefish win mates with transvestite antics

Cuttlefish may be the most talented quick-change artists in the animal kingdom. Single males can adopt a sophisticated feminine disguise to help them get near females that are guarded by large males.

Now researchers have proved that the mimics, who can change their appearance instantaneously, are successfully mating with such females.

Each year, during the winter, thousands of giant Australian cuttlefish (Sepia apama) gather on the southern coast of the continent to mate. The competition between males for the females is intense. On average, four males fight over each female, but the ratio can be as high as eleven to one.

“The rate at which they are able to change their appearance is incredible.”

Bryan NeffBehavioural ecologist, University of Western Ontario in Canada

The winner of each challenge, usually a large male, guards his mate closely. But smaller males still manage to secure about a third of all matings. There is a range of tactics from which a 'sneaker' male can choose. The options include waiting until the consort male is busy fending off a challenge; meeting his mate under a rock as she prepares to lay an egg; and disguising oneself as an female.

The latter approach is an "elaborate trickery", according to Roger Hanlon, a marine biologist with the Woods Hole Marine Biological Laboratory. To be convincing, the mimic has to take on a mottled colouring, hide some of his arms and alter the shape of the visible ones.

Cuckolding consorts

Although the practice has been seen before, until now no one had proved that it works, that is, that the sneaker males actually manage to fertilize the target females.

So Hanlon and his colleagues watched the behaviour of five female mimics off a rocky reef in northern Spencer Gulf, South Australia. They found that in 30 out of 62 attempts, the mimics deceived the guard male and got close to females. The researchers used DNA fingerprinting to show that two of the mimics succeeded in making a female pregnant, they report in Nature this week1.

The team also found that the mimics could change their appearance as fast as 10 times in 15 minutes. "The level of sophistication of mimicry is amazing," says Bryan Neff, a behavioural ecologist at the University of Western Ontario in Canada, "and the rate at which they are able to change is incredible."

Sexual mimicry is not new to the animal world. Both bluegill sunfish (Lepomis macrochirus) and red-sided garter snakes (Thamnophis sirtalis parietalis) are known to make use of it, for example. But male cuttlefish are the only animals known that can turn the change in physical appearance on and off so quickly.